The proposed work, to be a combined experimental and theoretical effort of two groups, aims to provide a foundation for predicting molecular solubilities within "interphases" of matter, especially the stationary hydrocarbon phases of leversed Phase Liquid Chromatography, (RPLC), and including amphiphilic aggregates such as lipid bilayer membranes, vesicles, and micelles. We have previously developed statistical mechanical theory to predict molecular organization in membranes and micelles. Predictions are in good agreement with results of x-ray diffraction, small angle neutron scattering, 2H, 13C, 19F NMR, and equation of state measurements. The principal conclusion is that chain molecule interphases are not bulk phases of matter, but bear close resemblance to interfacial phases. Bulk phase thermodynamics of colligative properties and of partition coefficients is not applicable to these systems; here we aim to develop more appropriate thermodynamic and statistical mechanical theory for solubilities in interphases. Our experimental efforts have been directed toward both theoretical and applied characterization of chromatographic systems. Here, we aim to test rigorously theoretical models through systematic study of solute size and chemical character, chain length and surface density of the grafted interphase chains, and through the establishment of valid reference states. This work should have direct bearing on: i) Retention mechanisms of RPLC, the most widely used and rapidly growing method of chromatographic separation, and ii) Fundamental physical chemistry of colligative properties of lipid bilayers, vesicle, and biological membranes, and may provide a foundation for understanding molecular mechanisms of anesthetic drug action.